In the field of orthopedic surgery, it is common to rejoin broken bones. The success of the surgical procedure often depends on the successful reapproximation of the bone fragments, the amount of compression achieved between the bone fragments, and the ability to maintain that compression between the bone fragments. If the surgeon is unable to bring the bone fragments into close contact, a gap will exist between the bone fragments and the bone tissue will need to fill that gap before complete healing can take place. Furthermore, gaps between bone fragments that are too large allow motion to occur between the bone fragments, disrupting the healing tissue and thus slowing the healing process. Optimal healing requires that the bone fragments be in close contact with each other, and for a compressive load to be applied and maintained between the bone fragments. Compressive strain between bone fragments has been found to accelerate the healing process in accordance with Wolf's Law.
Broken bones can be rejoined using screws, staples, plates, pins, intramedullary devices, and other devices known in the art. These devices are designed to assist the surgeon with reducing the fracture and creating a compressive load between the bone fragments. Intramedullary devices are often used for fractures of the long bones; however, they are also frequently used in the phalanges and specifically for the treatment of “hammer toe”, which is a deformity of the proximal interphalangeal joint of the second, third, or fourth toe causing the toe to be permanently bent. Typical intramedullary devices used in the phalanges have opposing ends that are adapted to grip against the wall of the intramedullary canal. These intramedullary devices are typically made of titanium alloys, stainless steel alloys, Nitinol and other materials, e.g., PEEK. The titanium alloy devices and stainless steel alloy devices often have barbs or threaded regions at their opposing ends to grip the wall of the intramedullary canal. The Nitinol devices typically have a pair of radially extending “legs” at their opposing ends that expand outward when warmed to body temperature, with the pair of legs at each end being disposed in a common plane.
While these intramedullary devices are designed to bring the bone fragments into close contact and to generate a compressive load between the bone fragments, these devices do not always succeed in accomplishing this objective. The compressive load dissipates rapidly as the bone relaxes and remodels. Furthermore, gripping the bone with only a pair of coplanar legs does not provide significant torsional stability to the fusion site.
Thus, there exists a clinical need for intramedullary devices that are better able to bring bone fragments into close proximity with each other, generate a compressive load, and maintain that compressive load for a prolonged period of time while healing occurs.